Almost every industrial solar project that disappoints was decided badly before anyone climbed onto a roof.
Solnce runs a marketplace. Over 1,000 projects have gone through it, across more than 35 onboarded EPC companies and 21 cities. That position gives us an unusual view: we see the same specification quoted by different contractors, and we see what happens to those projects two, three and five years later.
The failures are remarkably consistent. Nine mistakes account for most of them, and eight of the nine are made at the procurement stage — before a contract exists, when they are still free to fix.
1. Confirming your metering regime last, instead of first
The most expensive assumption in Indian C&I solar is that net metering is available to you.
For a commercial consumer in Tamil Nadu, it is not — LT non-domestic consumers are restricted to net feed-in. In Uttar Pradesh, net metering is available only to metered domestic and metered agricultural connections; every commercial and industrial consumer is on gross metering or net billing. Gujarat caps commercial systems at 50% of sanctioned load. Telangana caps at 80% of contracted demand and applies the most restrictive distribution transformer loading limit in India at 50%.
A savings model built on units × your tariff is correct only under net metering. Under net billing you sell exported units at a regulated rate — ₹3.65/kWh in Rajasthan against a retail tariff several rupees higher — which changes both the return and the optimal system size.
Fix it before anything else. Ask for your regime, your capacity cap, your export rate and your settlement period in writing, and require the savings model to be rebuilt on those numbers if it wasn’t.
2. Comparing three quotes that aren’t comparable
This is the single most common procurement failure we see, and it is structural rather than anyone’s fault.
Three EPCs quote in three formats. One includes the net meter and DISCOM liaison; one doesn’t mention it. One specifies 80-micron hot-dip galvanisation; one says “GI structure.” One quotes 545 W modules by make and model; one says “Tier-1 mono PERC.” The cheapest number wins, and nobody has established what was removed to get there.
Fix it: issue one specification and require all bidders to respond against it, line by line. If you are not running a formal tender, a one-page comparison sheet with fixed rows — module make and model, inverter make and model, structure spec and galvanisation thickness, DC and AC cable sizing, connector brand, net meter scope, DISCOM liaison scope, warranty terms split, PR guarantee, O&M scope and duration — will surface the differences in an afternoon.
This is most of what our platform does. You can do it yourself with a spreadsheet; what you cannot do is compare three unlike documents by reading them.
3. Taking “25-year warranty” at face value
Every module carries two warranties and they are not the same thing.
The product warranty — covering defects in materials and workmanship, delamination, junction box failure, frame corrosion — runs 10 to 12 years on Indian modules, 15 on some premium lines. The performance warranty, guaranteeing measured output at standard test conditions stays above a defined curve, runs 25 to 30 years.
A quotation that says “25-year warranty” without distinguishing them is being loose with you, and you will discover which one you actually have in year thirteen.
MNRE’s SOP of 6 May 2026, as reported, sets the floor for scheme projects at a minimum 10-year product and 25-year performance warranty, with the warranty running from installation only if that occurs within six months of the manufacturer’s invoice — otherwise reduced proportionately. That clause exists because aged stock was being installed.
Fix it: require both terms stated separately in the quotation, and demand the actual warranty certificates at handover, not a brochure.
4. Not requiring a Performance Ratio guarantee
Ask what generation you are being promised and how it will be measured. If the answer is a CUF figure, you have a weak instrument.
CUF — annual generation over rated capacity times hours in the year — takes no account of irradiance, temperature or grid availability. A contractor who guaranteed 18% CUF and delivers 15% in a poor monsoon year has a complete weather defence.
Performance Ratio normalises for the sunlight that actually reached your array. It captures thermal losses, soiling, cabling, inverter conversion, mismatch and downtime — everything inside the contractor’s control — and excludes everything outside it.
For reference, the PM Surya Ghar model agreement requires 75% PR at commissioning, maintained for five years, and requires the vendor to supply a calibrated radiation sensor at commissioning to establish it. That is the floor for a subsidised residential system. A well-engineered industrial plant should run in the 75–82% band.
Fix it: specify PR, not CUF. Specify how and when it will be measured. Specify what happens if it isn’t met.
5. Discovering the roof after the contract
Older industrial roofs — pre-engineered buildings, asbestos sheeting, aged trusses — are the most common technical constraint on factory rooftop solar, and the most common source of variation claims.
A 2 MW roof with 900 kW of unshaded, structurally sound area is a 900 kW project. You should learn that during feasibility, not during execution.
Fix it: require a structural assessment signed by a licensed engineer before contract, not a spreadsheet estimate afterwards. Require the mounting design to be verified by a licensed structural designer, which is a requirement in most state DISCOM specifications anyway. And settle the waterproofing methodology and retention in the contract — roof penetrations on industrial sheeting are where the complaints start in year two.
If the roof genuinely cannot carry the array, ground-mounted on spare land alongside the shed is often cheaper than reinforcing a twenty-year-old truss.
6. Value-engineering the parts you cannot see
When a quote comes in materially under the field, the saving is almost never in the modules. It is in the components nobody inspects.
DC connectors. Testing of field-aged connectors pulled from Indian utility and rooftop plants found units in service six years or more in harsh climates running at 300% of initial contact resistance under thermal cycling and up to 600% under damp heat, against a permissible limit of 150%. The same work documented counterfeit connectors in the field, inconsistent markings and mixed-brand mating. Connector failure causes ground faults and fires — this is a safety item before it is a yield item.
Cable sizing. Undersized DC and AC cable is invisible on a quotation and shows up as voltage drop for twenty-five years. Specify a maximum of 2%.
Structure galvanisation. Eighty microns of hot-dip is the common specification. Sixty is cheaper and you will not see the difference for six years, particularly in a coastal or industrial atmosphere.
Earthing. Potential-induced degradation was found at 7 of 36 Indian sites in the national reliability survey and identified as the leading cause of accelerated degradation at sites under five years old. It is closely tied to grounding quality. Specify earthing to IS 3043:2018 and require measured earth resistance recorded at handover.
Fix it: specify a single matched connector brand, factory-crimped where possible; state the galvanisation thickness in microns; state the maximum voltage drop; and require commissioning tests to IEC 62446-1 documented and handed over — string open-circuit voltages, insulation resistance, earth continuity, polarity.
7. Designing to nameplate instead of to your load curve
A single-shift plant that exports heavily on Sundays gets a very different answer under net billing than under net metering. A three-shift continuous process plant on a compact footprint offsets a much smaller proportion of consumption than a single-shift unit with generous roof.
In states with time-of-day tariffs, the value of a solar unit varies through the day, and the design should reflect that.
Fix it: give your EPC twelve months of bills and, if you have them, half-hourly or shift-level consumption data. A system sized against your actual load curve will outperform one sized against your roof area, even if it is smaller.
8. Building a group captive structure on rules that changed in March
If you buy power through a group captive arrangement, the rules you were compliant with in February are not the rules you are compliant with now.
The Electricity (Amendment) Rules, 2026, notified 13 March 2026, substituted Rule 3 of the Electricity Rules, 2005 entirely. The 26% and 51% thresholds survive, but the 51% test is now assessed collectively across all captive users rather than user by user — which removes the risk that one minority user’s shortfall de-captivates the plant for everyone.
The half that costs money: from 1 April 2026, an individual captive user’s consumption is admissible only up to 100% of its proportionate share, with the excess treated as supply by a generating company and attracting cross-subsidy surcharge and additional surcharge. Users holding 26% or more are exempt from that cap.
There is no grandfathering. Existing structures are not preserved.
Fix it: if your anchor consumer sits below 26% and consumes more than its proportionate share, model the exposure now. We have written up all four of the worked examples the government published in Schedule III — read the group captive guide.
9. Treating renewable obligation as the DISCOM’s problem
It isn’t, any more.
The Renewable Purchase Obligation has been superseded by the Renewable Consumption Obligation, notified in September 2025 under the Energy Conservation Act. Designated consumers who take power from a captive plant or through open access are directly obligated, to the extent of that consumption — with penalties adjudicated by your State Electricity Regulatory Commission.
The target is 35.95% in FY 2026-27, rising to 43.33% by FY 2029-30. Sector thresholds for designation are lower than most managers assume: 3,000 MTOE for textiles and chemicals, 1,500 for forging, 2,500 for dairy.
And a detail worth knowing: rooftop solar on your own factory counts as distributed renewable energy, needs no open access approval, and is usually the cheapest compliant unit available to you.
Fix it: establish whether you are designated before you treat solar as discretionary. The RCO guide is here.
The tenth mistake, which is about timing
Solar assets attract accelerated depreciation at 40% on written-down value, against 15% for general plant and machinery. But where an asset is put to use for fewer than 180 days in the tax year, the allowance is restricted to half the prescribed rate in year one — which puts the practical cutoff for a full-rate claim at around the start of October.
An industrial rooftop project typically runs 8 to 16 weeks from order to commissioning, with DISCOM approvals and structural strengthening the usual critical path items.
We are not going to pretend that helps you if you are reading this in late August. It is the reason to start the FY 2027-28 conversation in June rather than December.
Please confirm your position with your chartered accountant — the Income-tax Act, 2025 came into force on 1 April 2026 and provisions have been renumbered.
What good procurement looks like
Six things, in order:
1. Twelve months of bills and a load profile — before anyone quotes
2. Your metering regime confirmed in writing — regime, cap, export rate, settlement period
3. A structural assessment signed by a licensed engineer — before contract
4. One specification, multiple bidders, one comparison format
5. A contract that states PR, both warranty terms, the O&M scope and the commissioning test protocol
6. A handover file — commissioning tests to IEC 62446-1, serial numbers, as-built drawings, warranty certificates, measured earth resistance
That sequence costs a few weeks at the front and removes most of what goes wrong over twenty-five years.
If you would like us to run step four for you — one specification, multiple verified EPC partners, one comparison format — send us your last twelve months of bills and a roof drawing or satellite view.
Frequently asked questions
1. How long does an industrial rooftop solar project take? Typically 8 to 16 weeks from order to commissioning for a system in the hundreds of kW. DISCOM approvals and, where required, structural strengthening are the usual critical path items — not the installation itself, which is a matter of days.
2. What should an industrial solar quotation contain? Module make, model and wattage; inverter make and model; structure specification with galvanisation thickness in microns; DC and AC cable sizing with maximum voltage drop; connector brand; net meter and DISCOM liaison scope; both warranty terms stated separately; a Performance Ratio guarantee; and the O&M scope and duration.
3. How do I compare EPC quotes that are in different formats? Issue one specification and require all bidders to respond against it line by line. If you are not running a formal tender, build a fixed-row comparison sheet covering the items above. Comparing three unlike documents by reading them is not possible.
4. Should I insist on a Performance Ratio guarantee or a CUF guarantee? Performance Ratio. CUF ignores irradiance, temperature and grid availability, which gives a contractor a weather defence. PR normalises for the sunlight that actually reached the array and captures only what is within the contractor’s control.
5. What Performance Ratio should an industrial plant achieve? A well-engineered, well-maintained Indian system should run in the 75–82% band annually. For reference, the PM Surya Ghar model agreement requires 75% at commissioning maintained for five years on subsidised residential systems.
6. Do I need a structural assessment before installing rooftop solar? Yes, and before contract rather than after. Modules and structure add dead load, wind uplift adds considerably more, and older pre-engineered buildings and asbestos sheeting are the most common technical constraint. Most state DISCOM specifications require the mounting design to be verified by a licensed structural designer in any event.
7. Why are some solar quotes so much cheaper? Rarely because of the modules. Look at connector brand and crimping method, DC and AC cable sizing, structure gauge and galvanisation thickness, and earthing specification. These are invisible on a quotation and account for most of the price spread.
8. What commissioning tests should I insist on? Commissioning to IEC 62446-1 — string open-circuit voltages, insulation resistance, earth continuity, polarity and protection function — documented and handed over. Plus measured earth resistance recorded at handover, given the link between grounding quality and potential-induced degradation.
9. What is the difference between product warranty and performance warranty? Product warranty, typically 10 to 12 years on Indian modules, covers defects in materials and workmanship. Performance warranty, typically 25 years, guarantees measured output at standard test conditions stays above a defined curve. A quotation citing a single “25-year warranty” is conflating them.
10. Can I install more solar than my sanctioned load? It depends on your state. MNRE advised DISCOMs in March 2026 to allow up to 10% tolerance in DC capacity provided inverter AC capacity stays within sanctioned load. Several states additionally cap commercial systems as a proportion of sanctioned load — Gujarat at 50%, Punjab at 70%, Telangana at 80% of contracted demand.
11. Do the group captive rules affect an existing structure? Yes. The Electricity (Amendment) Rules, 2026 contain no grandfathering. From 1 April 2026 an individual captive user’s consumption is admissible only up to 100% of its proportionate share unless it holds 26% or more, with the excess attracting cross-subsidy surcharge and additional surcharge.
12. Is my factory obligated under RCO? If you are a designated consumer under your sector’s MTOE threshold and you consume from a captive plant or through open access, yes — to the extent of that consumption. Thresholds are lower than many assume: 3,000 MTOE for textiles and chemicals, 1,500 for forging.
13. Does rooftop solar on my own factory count toward RCO? Yes. Eligible non-fossil generation of 10 MW or less qualifies as distributed renewable energy, expressly including behind-the-meter systems, and it needs no open access approval.
14. When must an industrial system be commissioned to claim full-rate depreciation? Solar assets attract 40% accelerated depreciation on written-down value, restricted to half the prescribed rate where the asset is put to use for fewer than 180 days in the tax year — which puts the practical cutoff at around the start of October. Confirm with your chartered accountant, particularly as the Income-tax Act, 2025 came into force on 1 April 2026.
15. Should we do CAPEX or OPEX? If you have capital and taxable profits to absorb depreciation, CAPEX usually produces better lifetime economics. If capital is constrained or you would rather not own a generating asset, OPEX shifts that to a developer at the cost of a long-term contract on your roof. Model both with your own numbers rather than accepting a rule of thumb.
16. What should be in the handover file? Commissioning test results to IEC 62446-1, module and inverter serial numbers, as-built layout and electrical single-line diagram, structure design drawing, warranty certificates for all major components, measured earth resistance, and monitoring system access. Insist on it before releasing final payment.
